Charge Your Phone (and Your Car) from Afar

Charge Your Phone (and Your Car) from Afar

Over the air: Witricity’s CEO Eric Giler holds a light that is powered remotely by the pad behind it.

Eric Giler points a remote control at a small black pad leaned up against a wall, and three lamps instantly light up and a tablet computer starts charging. The funny thing is, the devices all sit several feet away from the black pad, which provides power, and aren’t plugged in.

Giler is the CEO of Witricity, a startup that hopes to revolutionize electronics by replacing wireless charging systems with ones that send power safely through the air. The nearly five-year-old company uses technology developed at MIT that extends the range of inductive wireless charging.

Witricity says its first products—for charging portable electronics—could be on the market later this year. Within a year or two, similar technology could allow electric-vehicle owners to charge their cars without plugging them in. This could be followed by wireless power for heart pumps and other medical implants.

The idea of wireless power transfer is hardly new. Nikola Tesla demonstrated a version of it a hundred years ago, and inductive chargers for electric toothbrushes and video game controllers are now widespread. But the inductive chargers available today work over only very short distances and require physical contact between the charger and electronic device, which isn’t much more convenient than plugging a device in.

Inductive charging systems work by passing a current through a coil to generate a magnetic field, which creates another electric current in a similarly sized and oriented coil in the other device. Move these coils apart, and the efficiency of energy transfer drops off quickly. To increase the distance at which the power is transferred efficiently, Witricity tunes the sending and receiving coils to resonate with each other at a specific frequency with very little energy loss within each resonator.

The distance that power can be transferred in this way depends on the size of the coils. If both the sending and receiving coils are small, as may be the case with a system for mobile phones, the charger and the phone need to be placed within several centimeters to charge efficiently. But Witricity has also shown prototypes with larger coils that can send power at distances of about a meter. (Power can also be beamed with lasers and microwaves, but this requires a direct line of sight and can raise safety concerns.)